红光QLED顶发射器件中上电极的构筑与性能研究
Study on the Construction and Performance of the Top Electrode in Red-Emitting QLED Top-Emitting Devices

量子点是一种半导体纳米晶体，因其发光波长可调、颜色纯度高、色域广、寿命长、可溶液法制备受到广泛关注。量子点发光二极管(QLED)以其优越的发光性能、高效的能量转换效率，成为下一代平板显示、照明和可穿戴设备等领域的候选方案。顶发射是一种发光二极管结构，最后蒸镀的电极方向即为出光方向，不同于底发射，它的出光不需要经过驱动薄膜晶体管(TFT)，因此其开口率高，是OLED/QLED显示的一种选择方案。顶发射QLED从顶电极一侧出光，因此，提高顶电极的出光效率是一个重要课题。通常在顶部电极上覆盖一层光提取层(Extraction Layer, EXL)，调整功能层和光提取层之间的折射率差异，以提高出光率，同时采用光散射层(Scattering Layer, SCL)抑制微腔效应造成的出光角度不均匀问题。但是，通过调整功能层厚度来匹配光提取层折射率的方法会使得器件的电荷平衡性遭到破坏，同时现有的光散射层的制备过程涉及光刻、刻蚀等工艺，比较复杂，也易破坏器件功能层。基于此，本论文研究了光提取材料的筛选原则，使用了与量子点发光层折射率相匹配的光提取材料，优化光提取层厚度，提升了器件电流效率。另外，通过旋涂工艺，引入了光学纳米材料对出光施加散射，对比发现，粗糙度更大的纳米颗粒能够显著抑制光的角度分布不均匀问题。实验结果显示，优化后的顶电极结构使得器件的电流效率从14.8 cd/A提升到17.9 cd/A，而且器件的出光角度更加分散。
Quantum dots are semiconductor nanocrystals that have garnered significant attention due to their tunable emission wavelengths, high color purity, wide color gamut, long lifetimes, and solution-processable fabrication. Quantum dot light-emitting diodes (QLEDs), renowned for their superior luminescent properties and high energy conversion efficiency, are emerging as potential candidates for next-generation flat-panel displays, lighting, and wearable devices. Top-emission is a type of light-emitting diode structure where the direction of the light emission corresponds to the direction of the final deposited electrode. Unlike bottom-emission, top-emission does not require the light to pass through the driving thin-film transistors (TFTs), resulting in a higher aperture ratio, making it a viable option for OLED/QLED displays. In top-emission QLEDs, light is emitted from the top electrode, making the improvement of the top electrode’s light extraction efficiency a critical issue. Typically, a light extraction layer (EXL) is applied over the top electrode to enhance light extraction by adjusting the refractive index difference between the functional layer and the light extraction layer. Additionally, a scattering layer (SCL) is used to mitigate the uneven light emission angle caused by the microcavity effect. However, adjusting the functional layer thickness to match the refractive index of the light extraction layer can disrupt the device’s charge balance. Furthermore, the current preparation process for scattering layers involves complex techniques like photolithography and etching, which can damage the functional layers of the device. In this context, the present study investigates the selection criteria for light extraction materials. By employing light